Lamp bulb



FIG. 1 is a front elevational view of a lamp bulb showing my new design (rear elevational view corresponds);

FIG. 2 is a left side elevational view thereof (other side corresponds);

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a bottom plan view thereof. 

The ornamental design for a lamp bulb, as shown and described. 